Pro's & Con's of fixed vs handheld dfc/vhf radio's

[Scary Des]

Originally Posted by gingercoastie

Actually it is ducting.

What's that??
Des

[gingercoastie]

Here goes,

High pressure keeps the radio signal trapped near to the Earths surface. As it still needs to go somewhere its range is increased. Imagine squashing a soft ball, its radious will increase.

[philip]

Originally Posted by gingercoastie

High pressure keeps the radio signal trapped near to the Earths surface. As it still needs to go somewhere its range is increased. Imagine squashing a soft ball, its radious will increase.

Fascinating - I'd always rationalised the high pressure improvements as due to there being less interference from water particles in clouds mist etc with a high pressure .

Thanks for that Mr Coastie

[Powerboat]

Hi Brendan,

If you look at Jon Broks later post you'll see where I was coming from with my 2 to 3 watts. Real output as opposed to nominal out put based on all the variables that Jon describes...connections, length of cable run, corrosion , type of antennae etc.

In my other career I'm a Signals Officer in the Army and so would have quite a lot of experience with hand held and fixed VHF both marine and otherwise.

Regularly when you test older kit you can find actual radiated output power from the antenna to be down on 50% of what you expect.

While endorsing all of what Jon has said I would tend to be more cautious on the miles and would "generally" say 3 to 5 miles for hand held and 15 miles for a RIB mounted Fixed VHF in good condition. The ranges quoted in RYA manuals are often based on sailing yachts with a much higher mast !! Again as Jon rightly says there are so many variables !!!

Not scientific ............but I did a test a few years ago .Me with a hand held swimming in the middle of one of the large Shannon Lakes at night with a one metre short chop had good Stength 5 comms with a fixed unit in one of the Boat Squad RIBs 3 miles away.

We have a saying in my unit which is " Promise less - Deliver more !!" or err on the side of caution !



Kind regards,

Stuart

Originally Posted by BrendanS

Not worried about the "."

Most people can surely work out that fixed is 25W. What concerned me is that you thought handhelds worked at 1-2W? Yes, as you say, handhelds work at 1W at times, but either you have to select a channel where that kicks in automatically, or select it yourself. The rest of the time it's typically 5W.

Anyway, I'm with you on having a fixed set with hand held for backup, but a hand held is far better than none at all. The next issue is taking the exam, and understanding these issues?

[BrendanS]

Originally Posted by Rogue Wave

where are the masts in the Solent other than at Lee.

That got me interested. I thought Needles had masts, but not sure? Do they have aerials at St Cats as well?

[BrendanS]

Originally Posted by Powerboat

Hi Brendan,

If you look at Jon Broks later post you'll see where I was coming from with my 2 to 3 watts. Real output as opposed to nominal out put based on all the variables that Jon describes...connections, length of cable run, corrosion , type of antennae etc.


Stuart

Err! but you actually said 1-2 watts, and we were talking handhelds, so no probs with length of cable run, connections etc. A good handheld rated for 5W will put out pretty much that

[BrendanS]

Originally Posted by Scary Des

I‘ve got to take the boat out later

My boat is Lymington too. Want to give this a crack? I've got cabin fever. I'll wear furry mid layer under drysuit this time, it got bleedin cold last time. If we can't get three boats out, I'll hang off a line from my boat while you do distance work. Serious!

[Jon Brooks]

The other thing with any hand held is that is standard antenna is not very efficient.

We try to make them as good as we can but its all about the "laws of physics Jim"

You are taking a 1/4 wave whip and turning it into a compressed spring.
So you have approx 450mm of wire wound into a length of 160-180mm.

The 5w is what comes out of the top of the unit not the top of the antenna.

So if it is a very poor helicoil you could end up with an ERP (effective radiated power) of a fair bit less.
It would be an average of 3db loss (so half power) I have seen tested (not ours!) that have massive loss.
So you end up with a watt or less being radiated.

Some more helpful stuff for you to chew over!!

Regards

[Jelly]

Hi GingerCoastie & Des
Glad you got the Ducting bit done was going to mention that.
Best example I know was a shipping pilot in the persion gulf talking to a oil rig in N Sea and he had a hand held ( probbably throught a repeater I guess).
Now thats what you call a lift !! (Ham talk) only lasted 2-3 minutes.
Jelly

[Scary Des]

Originally Posted by BrendanS

My boat is Lymington too. Want to give this a crack? I've got cabin fever. I'll wear furry mid layer under drysuit this time, it got bleedin cold last time. If we can't get three boats out, I'll hang off a line from my boat while you do distance work. Serious!

It’s a plan , but we need the weather for 1 mtr waves, so any time during the summer I suppose.

Des

[gingercoastie]

For those really interested in "Ducting" I have found you a website.


http://home.cogeco.ca/~dxinfo/tropo_nwe.html

[Powerboat]

Hi Brendan,

I refer you to Jon's post below.

As someone who deals with hand helds and field VHF equipment daily for the last 20 years, I would instinctively think of 1 or 2 watts when thinking hand helds. Hence my mention earlier (Like Jon) of effective "radiated Power" or what makes it out of the antenna.

As we all seem to have said, there are a lot of variables once you introduce weather and people to an exact science ! So always I guess, err on the side of caution on your equipments capabilities!

Kind regards,

Stuart




QUOTE=Jon Brooks] The other thing with any hand held is that is standard antenna is not very efficient.

We try to make them as good as we can but its all about the "laws of physics Jim"

You are taking a 1/4 wave whip and turning it into a compressed spring.
So you have approx 450mm of wire wound into a length of 160-180mm.

The 5w is what comes out of the top of the unit not the top of the antenna.

So if it is a very poor helicoil you could end up with an ERP (effective radiated power) of a fair bit less.
It would be an average of 3db loss (so half power) I have seen tested (not ours!) that have massive loss.
So you end up with a watt or less being radiated.

Some more helpful stuff for you to chew over!!

Regards [/QUOTE]

[qcamel]

Do I get an award for starting this massive thread? It has helped though as my new handheld arrives on Tuesday and the fixed vhs will be purchased at the boat show and installed shortly after. Will go away now and try to think of another topic to get you all going.....

Ollie

[Powerboat]

Nice to know that there was a happy ending Ollie !!

Stuart

[BrendanS]

Originally Posted by qcamel

Will go away now and try to think of another topic to get you all going.....

Ollie

Excellent, this one was great fun!

[BrendanS]

Originally Posted by Powerboat

I would instinctively think of 1 or 2 watts when thinking hand helds.

Stuart, That's very reasonable in the context you quote, though most people are going to assume that low power has been selected, as that is what handhelds are rated in, 5W high power, 1W low power .....though as stated, power from aerial is somewhat different. I've always assumed handheld aerials to be pretty inefficient, but never seen any numbers around it before now.

Great informative thread, and look forward to meeting up with Des to try some experiments.

[Louise]

Cheers, Brendan and Des for having the guts to give it a try. Rather you than me!!! Let us know when it's happening - maybe we could all come and watch. It could be the start of a whole new section - Put To The Test By Real Ribsters! You could test something every month, say.

[jwalker]

Originally Posted by Louise

Hi Des - can't remember off hand. Will get Richard to post when he gets home - he usually has a better memory for these things than I do!

Louise, we won't accept anything other than the result of a real test.

[Louise]

[BrendanS]

Originally Posted by Jon Brooks

So if it is a very poor helicoil you could end up with an ERP (effective radiated power) of a fair bit less.

My experiment was with an M1 Euro V which I know gives better transmit and reception than many handhelds, so the figures I came up with (miles) had better be revised down for many sets! What does the Euro V transmit at the aerial?

If Des and I do the rough water test, we'd better accumulate a good selection of different sets to make it worthwhile (and all of them had better be waterproof, cos they are going in the water with me! )